Arteriovenous malformations (AVMs) are composed of abnormal arterial and venous vessels in the brain causing arteriovenous shunts of arterialized blood directly from pial arteries to draining veins. The hemodynamics of these lesions is not well-understood. Changes in blood flow and pressure are probably related to the natural history of AVMs and may also play a major role in AVM treatment. In this study intra-arterial pressure was measured in feeding arteries of AVMs using a microcatheter that had been placed for subsequent embolization treatment (201 measurements were performed in 95 patients before and after the embolization procedure). Results show a direct relationship between pressure changes and degree of embolization. Since pressure changes during the embolization procedure are relatively small, it seems unlikely that these changes are the direct cause of rupture and periprocedural bleedings.